The present invention relates to a valve timing control system for an internal combustion engine, and more specifically to a valve timing control system capable of promptly and reliably adjusting angular phase relationship between the engine crankshaft and a camshaft in response to variation in load condition of an internal combustion engine.
U.S. Pat. No. 4,535,731 issued on Aug. 20, 1985 to Banfi and U.S. Pat. No. 5,088,456 issued on Feb. 18, 1992 to Suga disclose a valve timing control system for an internal combustion engine. The valve timing control system includes a cylindrical outer rotary member rotatable with a timing sprocket that is driven via a timing belt or chain by a crankshaft of an engine. The valve timing control system also includes a cylindrical inner rotary member disposed within the outer rotary member and fixedly connected to the camshaft and a helical piston disposed between the outer and inner rotary members. An angular phase relationship between the inner and outer rotary members is variable with an axial motion of the helical piston owing to a hydraulic pressure acting thereon.
Specifically, the valve timing control system disclosed in the U.S. Pat. No. 5,088,456 includes a floating piston movably disposed between the inner and outer rotary members and defining first and second chambers on its both sides. A valve spool movably disposed in the inner rotary member cooperates with a two-position solenoid operated flow control valve connected to a hydraulic fluid source, for selectively draining or communicating the first and second chambers with the hydraulic fluid source. When the engine load varies from a medium level to a high level, the first chamber is drained while the second chamber defined between the floating piston and the helical piston is supplied with a hydraulic fluid. Therefore, when the second chamber is expanded upon introduction of the hydraulic fluid thereinto, the floating piston is allowed to move remote from the helical piston. This leads to the deficiency that the hydraulic pressure exerted on the helical piston is not sufficiently large for quick motion of the helical piston.
Thus, the valve timing control system includes the two-position solenoid operated flow control valve and the two-position solenoid operated spool valve, resulting in the complicated structure and operational steps.
An object of the present invention is to provide a valve timing control system which a shift is made quickly.